1. Field of the Invention
This invention relates generally to a device positioning system for positioning surgical instruments and, more particularly, to a device positioning system for positioning surgical instruments that allows a surgeon to position surgical devices and instruments from a remote location so that fluoroscopic images can be taken of the instrumentation relative to the patient without exposing the surgeon to radiation.
2. Discussion of the Related Art
A number of studies have shown the benefits of maintaining the posterior supporting anatomical architecture of the spine when performing spine surgery. Traditional approaches used for posterior spinal instrumentation involve detaching the muscular and ligamentous attachments from the spine in order to visualize and palpate the bony anatomy when placing pedicle screw instrumentation. In doing so, significant harm is done to the muscles and ligaments, which can result in muscle atrophy and reduced function. Numerous studies have shown the detriment of posterior retraction of the multifidus and erector spinae muscles while performing spine surgery. Additionally, devascularization, denervation, and injury to the adjacent facet joint during traditional open procedures have been shown to result in transitional syndrome leading to canal stenosis.
As a result of transitional syndrome, patients frequently undergo additional surgery with the need for decompression and extension of the fusion and instrumentation to adjacent levels. The cascade of events can then re-occur on adjacent levels requiring additional surgery. Each additional spine surgery creates more scarring and the possibility of conditions, which are hard to treat, namely arachnoiditis and “failed back syndrome” can occur. These patients often represent the hardest group of patients in which to obtain favorable clinical outcomes and certainly have added to the perception that spine fusion surgery is not effective. Hypothetically, by surgically dissecting the supporting musculature and ligaments of the spine from the bone architecture, a relative instability is created between the fussed instrumented segments and the non-instrumented unfussed segments. Thus, the body may react by “laying down” tissue, i.e., the facets and ligaments hypertrophy, at the transitional zone to reduce the relative instability or non-physiologic motion. Significant hypertrophy of the facets and ligaments contribute to the transitional syndrome, which leads to canal and foraminal compromise and stenosis. Maintaining the posterior muscular and ligamentous anatomy reduces or eliminates this iatrogenic adjacent level instability.
In an attempt to prevent the cascade of events leading to “failed back syndrome” as well as maintaining the natural integrity of the spinous structures, minimally invasive spinal (MIS) instrumentation techniques have been developed. These techniques employ the use of fluoroscopic or image guidance navigation to facilitate pedicle screw instrumentation without the need for disruption of the midline structures of the spine. The benefits are numerous and include smaller incisions, maintenance of muscular and ligamentous attachments to the spine, no need to expose the spine, minimal blood loss, and safe and accurate pedicle screw application. Increasingly, studies have shown the clinical benefits of these procedures when treating patients suffering from chronic debilitation back and/or leg pain due to degenerative disc disease and spondylolisthesis, with or without spinal stenosis.
The instrument and equipment requirements for accurate percutaneous pedicle screw placement, many of which are available in the standard operating room setting, include: a lead drape including thyroid shield for the surgeon and operative personnel; lead glasses for surgeon and operating room personnel; radiolucent table and frame that permits adequate antero-posterior (AP) and lateral fluoroscopic visualization of the spine; cannulated instruments for pedicle screw placement; K-wire and K-wire driver; Jamshidi or pedicle access device; and specialized instrumentation for percutaneous pedicle screw placement.
The patient is positioned prone on a radiolucent frame or a Jackson table. The Jackson table, with its relatively unencumbered area below the table platform, is ideal particularly when targeting the S1 pedicle using a Ferguson view since the gantry of the C-arm may require it to be positioned at a significant angle with respect to the table. Tables with a central platform base might inhibit this C-arm position when visualizing the S1 pedicles in particular. Once positioned, the C-arm is sterile draped to provide anterior-posterior (AP) and lateral images without contaminating the field when repositioning the fluoroscopic unit from an AP to lateral view.
After the necessary bone graft material is placed, the fluoroscopic unit is brought into the surgical field to view an AP image of the spine. The first step in accurately cannulating the pedicle is to position the C-arm to look down the pedicle. This is performed in the AP fluoroscopic view by placing the targeted vertebrae in the center of the fluoroscopic image seen on the monitor to prevent parallax distortion. The junction of the lateral facet and transverse process is targeted. A lateral fluoroscopic view determines the depths of the tip of the Jamshidi needle. The skin can be marked using a radio-opaque instrument to determine the entrance incision on the skin prior to targeting the pedicle.
The C-arm in the AP view is positioned on the coronal plane to look straight down the targeted pedicle. This is achieved by making sure that the end plate of the targeted vertebral body is viewed as one line, i.e., the vertebral body is not tilted in the AP view of the coronal plane, and the spinous processes are positioned in the midline. Magnification of the targeted vertebrae is also helpful. Once adequately positioned, the two pedicles on the vertebral body should be clearly visualized. Especially important is to view the medial border of the pedicle since violating this border by either a K-wire or targeting needle can result in nerve root injury. Viewing the pedicles on adjacent vertebral bodies above or below the targeted level can help to delineate the anatomy of the targeted pedicle. This is particularly helpful when targeting the sacrum (S1) where the pedicle can be hard to visualize since the relative absence of the rostral or superior and lateral border of the pedicle exist.
One of the main difficulties in assessing pedicle screws is having an accurate intraoperative method to confirm pedicle screw placement. Traditionally, screws are placed free hand with the use of anatomic markers.
In an attempt to improve the accuracy of pedicle screw placement, computer-assisted image guidance has been advocated. The underlying accuracy of the available image guidance technology may, however, be inadequate to place screws successfully at certain spine levels. Therefore, the need for accurate image-guidance navigational systems that can assist surgeons in placing pedicle screws accurately is needed. It has been found that the availability of intraoperative electrophysiological techniques, i.e., intraoperative pedicle screw stimulation, are extremely helpful in performing safe and accurate percutaneous pedicle screw placement. Medial placed screws or K-wires that impinge upon the nerve root can be identified using intra-operative electrophysiological monitoring. This would be detected by a relatively low action potential seen on intra-operative electromyographic (EMG) recordings.
The proper positioning of the patient on an operative table is required that provides for clear fluoroscopic visualization of the pedicles in the AP and lateral views. Adequate knowledge of the use of a fluoroscope to improve visualization of the pedicles for targeting is also necessary. Also, positioning of the fluoroscopic C-arm to view pedicles of each particular pedicle targeted is necessary. In patients with a deformity, such as scoliosis, particular attention must be paid to adequately position the C-arm. It is also necessary to protect both patient and operative room personnel from unnecessary radiation exposure by using an on/off technique when taking fluoroscopic images and step away from the operating table when possible.